H. Craig et al., NONEQUILIBRIUM AIR CLATHRATE HYDRATES IN ANTARCTIC ICE - A PALEOPIEZOMETER FOR POLAR ICE CAPS, Proceedings of the National Academy of Sciences of the United Statesof America, 90(23), 1993, pp. 11416-11418
''Craigite,'' the mixed-air clathrate hydrate found in polar ice caps
below the depth of air-bubble stability, is a clathrate mixed crystal
of approximate composition (N2O2).6H2O. Recent observations on the Byr
d Station Antarctic core show that the air hydrate is present at a dep
th of 727 m, well above the predicted depth for the onset of hydrate s
tability. We propose that the air hydrate occurs some 100 m above the
equilibrium phase boundary at Byrd Station because of ''piezometry''-i
.e., that the anomalous depth of hydrate occurrence is a relic of a pr
evious greater equilibrium depth along the flow trajectory, followed b
y vertical advection of ice through the local phase-boundary depth. Fl
owline trajectories in the ice based on numerical models show that the
required vertical displacement does indeed occur just upstream of Byr
d Station. Air-hydrate piezometry can thus be used as a general parame
ter to study the details of ice flow in polar ice caps and the metasta
ble persistence of the clathrate phase in regions of upwelling blue ic
e.